This invention relates to the production of arylene sulfide polymers. In one aspect, this invention relates to the production of phenylene sulfide polymers. In another aspect, this invention relates to the production of arylene sulfide polymers having a high extrusion rate. In a further aspect, this invention relates to the production of arylene sulfide polymers in which the functionality of the polymer end groups is controllable. In a still further aspect, this invention relates to arylene sulfide polymers having functionalized end groups.
A basic process for the production of arylene sulfide polymers from polyhalo-substituted aromatic compounds by reaction with an alkali metal sulfide in the presence of a polar organic compound is disclosed in U.S. Pat. No. 3,354,129. This patent also discloses that the molecular weight of the arylene sulfide polymers can be reduced by the use of monohalo-substituted aromatic compounds as chain terminating agents or by the use of an excess of one of the reactants, such as p-dichlorobenzene, in the polymerization reaction mixture. The use of excess dihalo-substituted aromatic compound reactant suffers from the disadvantages of increased cost of added reactant materials, difficulty in polymer recovery, and the need for recovering and recycling excess dihalo-substituted aromatic compound to the polymerization zone. In addition, previous attempts to employ monohalo-substituted aromatic compounds as chain terminating agents to obtain arylene sulfide polymers of reduced molecular weight have given generally unsatisfactory results because: (1) either the monohalo compound was so unreactive that it could not compete with the polyhalo-substituted aromatic compound monomer and thus had essentially no effect on the polymer produced in its presence, or (2) the monohalo compound, while activated relative to the polyhalo-substituted aromatic compound, possessed an activating group which was unstable under polymerization and/or polymer recovery conditions thus promoting polymer instability, or (3) the monohalo compound, while activated relative to the polyhalo-substituted aromatic compound, was relatively expensive compared to the polyhalo-substituted aromatic compound.
Control of functionality of end groups of arylene sulfide polymers is typically done by endcapping. In general, endcapping is accomplished by addition of an endcapping agent to the polymerization mixture at or near the end of the polymerization cycle and prior to the polymer recovery steps. the endcapping agent may also be added to the polymerization mixture earlier in the polymerization cycle. The appropriate addition time is dependent on the relative reactivities of the starting materials and the endcapping agent, the polymerization temperature and the desired molecular weight of the arylene sulfide polymer. For example, endcapping can be typically described as the preparation of functionalized arylene sulfide polymers by addition to the polymerization mixture of a functionalized monohalo aromatic having enhanced halide reactivity and containing the desired functional group.
U.S. Pat. No. 4,486,578 discloses the use of activated chloro- or bromobenzenes as evidenced by positive Hammet .sigma. values to introduce the functionality to arylene sulfide polymers. The problem with endcapping arylene sulfide polymers is that one is limited to nucleophilic chemistry starting with a sulfur source, e.g. Na.sub.2 S, and a dihaloaromatic, e.g. dihalobenzene. Generally, for nucleophilic reactions to displace halogen on a phenyl ring requires that it be activated by an electron accepting or attractive substituent somewhere on the ring. Such activating substituents can be deduced by looking at Hammett .sigma. values. Hammett .sigma. values which are positive (+) are considered electron accepting (activating) whereas a negative (-) value is electron donating (deactivating) and a value of 0 indicates no activation. While U.S. Pat. No. 4,486,578 also discloses the --COOH group, it is not applicable as an activating substituent as required in that patent because this form does not exist under arylene sulfide polymerization conditions. Instead, the salt form is present and the salt form would not be expected to react since it is not activating according to the criteria of U.S. Pat. No. 4,486,578.
It has now been unexpectedly discovered that non-activated or deactivated bromo- and iodobenzenes, i.e. Hammett .sigma. values which are 0 or negative respectively, are especially effective for endcapping arylene sulfide polymers to control the molecular weight of the arylene sulfide polymer and/or to introduce functionality to the arylene sulfide polymer chain.
Arylene sulfide polymers can be characterized at least in part in terms of a melt flow rate. It is generally considered that a melt flow rate is inversely related to molecular weight for polymeric materials in general and for arylene sulfide polymers in particular. Extrusion rate, which is more specifically defined hereinafter, is a specific type of melt flow rate which is particularly useful for characterizing arylene sulfide polymers in the lower molecular weight range.
Arylene sulfide polymers having a relatively high extrusion rate are desirable for a variety of applications such as encapsulation of electronic components and coating formulations. For example, U.S. Pat. Nos. 4,437,182 and 4,482,665 provide exemplary disclosures of compositions comprising arylene sulfide polymers which are employed in the encapsulation of electronic components.
Arylene sulfide polymers in which the functionality of the polymer end groups is controllable are desirable for improving surface adhesion properties of the polymer to metal substrates and/or fiber reinforcement. Such functionalized polymers are also desirable for increasing the crystallization rate of arylene sulfide polymers and for use in the preparation of copolymers by reaction at the polymer end groups having the desired functionality. The copolymers would be particularly useful as compatibilizers in polymer blends.